Most new bikes should come with one of these, but after a while, they will wear out.

This one is scaled to fit a 44mm diameter bottom bracket shell, but with the magic of 3d modelling, one could scale bigger or smaller as needed.

I have included a .3mf file with minimum amount of support material and good print settings, but one may want to decide for themself how to print it. There isn't really a particularly good orientation.

One small concern is that production cable guides are manufactured with a resin plastic so they wear in better. I personally don't know which filament is the best for this, but would reccomend ABS or ASA so that it's more durable outdoors. But at least this one costs about 20c in materials.